elsa-workflows/elsa-core · error · ArgumentException

A metadata key is required.

Error message

A metadata key is required.

What it means

ConsoleLogContextAccessor.PushMetadata stores a key/value metadata frame in the ambient log context. Both the key and the value must be non-whitespace; an empty or whitespace key throws ArgumentException naming the key parameter.

Solutions

1. Pass a non-empty, non-whitespace key (and value) to PushMetadata
2. Guard the call site: skip pushing when the key/value is missing instead of pushing empty strings
3. Fix the upstream source (e.g. configuration) that supplies an empty metadata key

Example fix

// before
accessor.PushMetadata(config.MetadataKey!, instanceId); // MetadataKey may be empty
// after
if (!string.IsNullOrWhiteSpace(config.MetadataKey))
    accessor.PushMetadata(config.MetadataKey, instanceId);

if (!string.IsNullOrWhiteSpace(key) && !string.IsNullOrWhiteSpace(value))
    accessor.PushMetadata(key, value);

bool CanPushMetadata(string? k, string? v) => !string.IsNullOrWhiteSpace(k) && !string.IsNullOrWhiteSpace(v);

try { accessor.PushMetadata(key, value); }
catch (ArgumentException ex) when (ex.ParamName is "key" or "value")
{ logger.LogWarning(ex, "Skipped empty console log metadata"); }

When it happens

Trigger: Calling PushMetadata("", value), PushMetadata(" ", value), or passing a null/whitespace key — directly or via PushWorkflowInstanceId when the workflow instance id source yields nothing and the key itself is blank.

Common situations: Programmatically building metadata keys from config values that are empty; a null instance id used as the key string; copy-paste leaving the key argument blank.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• A metadata value is required.
• The console log stream filter must be 'stdout', 'stderr'…
• The console log provider registration is invalid.
• Capacity must be greater than zero.
• Capacity must be greater than zero.

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/cff9a0d768976d96. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Diagnostics.ConsoleLogs/Services/ConsoleLogContextAccessor.cs:33

    private ConsoleLogContextAccessor()
    {
    }

    /// <inheritdoc />
    public IReadOnlyDictionary<string, string> GetMetadata()
    {
        var metadata = CurrentFrame.Value?.Metadata;
        return metadata == null || metadata.Count == 0
            ? Empty
            : new Dictionary<string, string>(metadata, StringComparer.OrdinalIgnoreCase);
    }

    /// <inheritdoc />
    public IDisposable PushMetadata(string key, string value)
    {
        if (string.IsNullOrWhiteSpace(key))
            throw new ArgumentException("A metadata key is required.", nameof(key));

        if (string.IsNullOrWhiteSpace(value))
            throw new ArgumentException("A metadata value is required.", nameof(value));

        var previous = CurrentFrame.Value;
        var metadata = previous?.Metadata != null
            ? new Dictionary<string, string>(previous.Metadata, StringComparer.OrdinalIgnoreCase)
            : new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);

        metadata[key] = value;
        CurrentFrame.Value = new(metadata);
        return new MetadataScope(previous);
    }

    /// <inheritdoc />
    public IDisposable PushWorkflowInstanceId(string workflowInstanceId) =>
        PushMetadata(ConsoleLogMetadataKeys.WorkflowInstanceId, workflowInstanceId);

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